Studies on the intracellular life history of immunoglobulin to be secreted or to be inserted into the plasma membrane of lymphocytes will be continued. Utilizing a new method for the detection of internally labeled cell surface immunoglobulin, we will determine the kinetics of transit to and shedding from the cell surface of various populations of lymphocytes. These studies will include the use of splenocytes from normal and axenic mice as well as thoracic duct lymphocytes from normal and x-irradiated, thymus-reconstituted animals. The biochemistry of cell surface Ig will be studied by peptide mapping to determine which portions of the molecule are exposed to the external millieu. The nature of the T cell receptor for antigen will be studied. These studies will involve the use of immune populations and specific immunoabsorbants as well as cell surface labeling using the lactoperoxidase technique.